1. Field of the Invention
The present invention is generally related to an exhaust system for a marine propulsion system and, more particularly, to an exhaust manifold and an exhaust elbow which are configured to separate the exhaust gas interface between the manifold and elbow from the coolant interface between those components in order to provide an elevated temperature at the interface and to decrease potential deleterious effects that could otherwise result from a coolant leak at the interface.
2. Description of the Prior Art
Marine propulsion systems are well known to those skilled in the art. In addition, exhaust systems for marine propulsion engines are also well known.
U.S. Pat. No. 4,866,934, which issued to Lindstedt on Sep. 19, 1989, discloses a marine drive exhaust system with shaped O-ring seals. The exhaust system is provided with resilient, shaped rubber O-ring seals between facing surfaces of the exhaust manifold and exhaust elbow and the facing surfaces of the exhaust elbow and the exhaust pipe. Each of the shaped O-ring seals has an inner peripheral rib extending peripherally around the exhaust passage and generally conforming to the shape thereof and begin spaced laterally between the exhaust passage and the peripheral water passages. Each of the shaped O-ring seals has an outer peripheral rib extending peripherally around the water passages and spaced laterally outward of the inner rib by a gap through which the water passages extend.
U.S. Pat. No. 6,290,558, which issued to Erickson on Sep. 18, 2001, discloses an exhaust elbow with a water trap,for a marine propulsion system. The elbow for a marine propulsion exhaust system is provided with a water trap section that defines a water collection cavity. Within the water trap section, a barrier extends downward into the water collection cavity to define first and second exhaust passages. When water begins to collect in the water collection cavity, the cross sectional area of the exhaust passage is reduced and the velocity of exhaust gases passing through the exhaust passage is increased. The water collection cavity is shaped to be easily cleared when exhaust gas pressure increases as the engine speed increases.
U.S. Pat. No. 6,077,137, which issued to Hahn on Jun. 20, 2000, describes an anti ingestion device. The device is intended for use with an engine, preferably a marine engine. The device comprises an exhaust manifold or riser system for exhausting engine gases, wherein the exhaust manifold has a first end and a second end, and the first end is connected to a cylinder head. There is a one-way pressure relief valve having a first end and a second end, wherein the first end is coupled to the exhaust manifold and the second end is exposed to atmospheric pressure. An air inlet line is coupled to the second end of the one-way pressure relief valve, such that the air inlet line serves as a conduit for guiding atmospheric pressure to the one-way pressure relief valve, thereby providing atmospheric pressure for passage into the exhaust manifold.
U.S. Pat. No. 5,133,185, which issued to Gilbreath et al on Jul. 28, 1992, describes an anti-moisture device for an engine exhaust. The device for removing moisture droplets from an interior surface of a duct, characterized by an outer edge secured to the interior surface of the duct, an inner edge surrounding an opening, and a connecting wall between the outer and inner edges is described. The inner edge of the anti-moisture device is positioned closer to a downstream end of the duct than the outer edge whereby the connecting wall is positioned at an angle relative to the interior surface of the duct. Moisture droplets traveling upstream will be caught between the connecting wall and the interior surface of the duct, on the downstream side of the device. The connecting wall is dimensioned so that a turbulent disturbance will be created along the interior surface of the duct whereby moisture droplets will be removed. The anti-moisture device is preferably made of a thermally conductive material so that moisture droplets contacting the device will be flashed into steam, or vaporized.
U.S. Pat. No. 4,526,002, which issued to Bibow on Jul. 2, 1985, discloses an exhaust relief system. The engine of a stern drive is provided with a vacuum relief valve to relieve any vacuum which may occur in the exhaust manifold, thus preventing water from entering the engine through the exhaust system. The relief valve is connected to allow one-way flow from the intake manifold to the exhaust system, thus providing an essentially closed system.
U.S. Pat. No. 4,991,546, which issued to Yoshimura on Feb. 12, 1991, describes a cooling device for a boat engine. A number of embodiments of cooling systems for internal combustion engines powering marine watercraft, wherein the engine cooling jacket delivers its coolant to an exhaust manifold cooling jacket adjacent the inlet end of the exhaust manifold and wherein coolant is delivered from the exhaust manifold cooling jacket to a further cooling jacket around the inlet portion of an exhaust elbow is described. In one embodiment, a closed cooling system is provided for the engine cooling jacket, exhaust manifold cooling jacket, and the elbow cooling jacket. In another embodiment, the system discharges coolant back to the body of water in which the watercraft is operating through a further cooling jacket of the exhaust elbow that communicates with its discharge end.
U.S. Pat. No. 5,109,668, which issued to Lindstedt on May 5, 1992, discloses a marine exhaust manifold and elbow. The marine exhaust assembly includes a manifold portion, an elbow portion, a water jacket portion, and exhaust runner walls, providing a smooth continuous transition of exhaust gas flow from intake exhaust passages in the manifold portion to transfer exhaust passages in the elbow portion around a bend to a discharge exhaust passage minimizing turbulent flow of exhaust through the manifold portion and elbow portion. Each transfer exhaust passage has its own water supply inlet at the upstream end of the respective intake exhaust passage. An upper vent includes a steam outlet opening in the water jacket at the high point of the elbow portion, and a steam exhaust channel extending along the top exterior of the water jacket portion in a raised bead above and parallel to an upper water flow passage and directing steam to the end of the discharge exhaust passage to mix with water and exhaust thereat. Water supports assist in directing cooling water up through the water jacket to the top of the elbow bend, and also prevent wall collapse during lost foam stainless steel casting.
U.S. Pat. No. 6,022,254, which issued to Neisen on Feb. 8, 2000, discloses an exhaust system for an inboard/outboard marine propulsion system. The exhaust system includes intermediate exhaust pipes which are physically separate components than the water separator. A sealed latching mechanism connects an outlet portion of the intermediate exhaust pipes to an inlet portion of the water separator. The sealed latching mechanism is secured yet flexible, and allows the orientation of the intermediate exhaust pipe to be adjusted relative to the water separator, thus allowing the exhaust system to be installed and serviced without dismounting or loosening the engine. The intermediate exhaust pipes also have a flared inlet part to facilitate alignment of the intermediate exhaust pipe at the exhaust elbow.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
One potential problem that can occur in an exhaust system of a marine propulsion system is the reverse flow of water within the exhaust conduits, in a direction from the body of water in which the marine vessel is operated back toward the exhaust manifold of the engine, resulting from negative pressure pulses s within the exhaust conduit. These negative pressure pulses can draw water in a reverse direction through the exhaust conduit toward the cylinders of the engine. Many different systems, including those described in U.S. Pat. Nos. 6,290,558 and 6,077,137, have been developed as modifications to the exhaust elbow structure to address this problem. In addition, an added device, such as that described in U.S. Pat. No. 5,133,185, has been developed for insertion between the exhaust manifold and the exhaust elbow in order to inhibit water from being drawn through the exhaust conduit in a reverse direction.
Exhaust systems for marine propulsion systems also experience a problem relating to the potential leakage of cooling water through the gasket between the exhaust elbow and the exhaust manifold. When this occurs in known exhaust systems, the water can flow from the coolant conduit of the exhaust manifold and exhaust elbow to the exhaust conduit of these components. The leakage of water through a failed gasket in this manner can allow water to leak into the exhaust manifold and, eventually,into the cylinders of the engine.
Both of these problems, described immediately above, relate to the passage of water into the cylinders of the engine. The water can cause serious damage if it is allowed to flow into the cylinders through open exhaust valves. The water can migrate to the region of the exhaust valves either by water inversion from the body of water in which the vessel is operated, in a reverse direction through the exhaust conduit, or alternatively, into the exhaust manifold from the water coolant system through a failed gasket between the exhaust manifold and the exhaust elbow.
It would be significantly beneficial if both of these water related problems could be solved. It would also be significantly beneficial if the exhaust passage from the exhaust manifold to the exhaust elbow were maintained at an elevated temperature in order to assist anti-moisture devices, such as that described in U.S. Pat. No. 5,133,185, to operate more efficiently.
An exhaust system for a marine propulsion engine, made in accordance with a preferred embodiment of the present invention, comprises an exhaust manifold which has an internal exhaust cavity formed within it and connectable in fluid communication with a plurality of cylinders of the engine for conducting exhaust gases away from the cylinders. It further comprises an internal coolant cavity, formed within the exhaust manifold, which is connectable in fluid communication with a coolant conduit of the engine for conducting coolant away from the coolant conduit of the engine. A first surface is formed on the exhaust manifold and the internal exhaust cavity intersects the first surface to form a first opening through which exhaust gases can flow out of the internal exhaust cavity of the exhaust manifold. A second surface is formed on the exhaust manifold and the internal coolant cavity intersects the second surface to form a second opening through which coolant can flow out of the internal coolant cavity of the exhaust manifold. The first and second surfaces are noncontiguous with each other.
In a particularly preferred embodiment of the present invention, the first and second surfaces are flat and disposed in a common plane. The present invention further comprises a first raised portion of the exhaust manifold. The first surface is disposed on the first raised portion. It further comprises a second raised portion on which the second surface is disposed. The first and second raised portions are spaced apart from each other to separate the first and second surfaces from each other.
A preferred embodiment of the present invention further comprises an exhaust elbow and an internal exhaust passage formed within the exhaust elbow which is connectable in fluid communication with the exhaust cavity of the exhaust manifold for conducting the exhaust gases away from the exhaust manifold. It also comprises an internal coolant passage formed within the exhaust elbow which is connectable in fluid communication with the internal coolant cavity of the exhaust manifold for conducting the coolant away from the internal coolant cavity of the exhaust manifold. A third surface is formed on the exhaust elbow and the internal exhaust passage intersects the third surface to form a third opening through which exhaust gases can flow out of the internal exhaust passage of the exhaust elbow. A fourth surface is formed on the exhaust elbow and the internal coolant passage intersects the fourth surface to form a fourth opening through coolant can flow out of the internal coolant passage of the exhaust elbow. The third and fourth surfaces are noncontiguous with each other. The third and fourth surfaces are flat, in a particularly preferred embodiment of the present invention, and are disposed in a common plane.
Third and fourth raised portions of the exhaust manifold are provided with the third and fourth surfaces being disposed on them, respectively. The third and fourth raised portions are spaced apart from each other to separate the third and fourth surfaces from each other. The first surface of the exhaust manifold is disposed in a posed facing relation with the third surface of the exhaust elbow and the second surface of the exhaust manifold is disposed in the posed facing relation with the fourth surface of the exhaust manifold. The exhaust elbow is rigidly attachable to the exhaust manifold.
A gasket is disposed between the first and third surfaces and between the second and fourth surfaces. In a preferred embodiment, the first, second, third and fourth surfaces are flat machine surfaces.
The gasket for an exhaust system, made in accordance with the present invention, comprises a metallic plate having an exhaust sealing segment and a coolant sealing segment. The coolant sealing segment is attached to and extends from the exhaust sealing segment. The exhaust sealing segment and the coolant sealing segment of the gasket each have first and second planar surfaces on opposite sides thereof. The first and second planar surfaces of the exhaust sealing segment are co-planar with the first and second planar surfaces of the coolant sealing segment, respectively. An exhaust opening is formed through the thickness of the exhaust sealing segment of the plate and first and second elastomeric seals are disposed on the first and second surfaces, respectively, of the coolant sealing segment. The first and second elastomeric seals are integral parts of a common elastomeric element. A raised portion of the exhaust opening through the metal plate extends at an angle from the exhaust sealing segment and away from the first surface to form a transition segment from a first opening of a first size, which is co-planar with the first surface, to a second opening of a second size, which is displaced from the first surface. The second opening is smaller in area than the first opening and, in a preferred embodiment, the transition segment is the shape of a frustum of a pyramid. A hole can be formed through the plate and located at a central region of the coolant sealing segment. The common elastomeric element can extend through the hole with the first and second elastomeric seals being joined to each other within the hole. The hole can be circular or, alternatively, a hole can be formed in the shape of an arc to serve the limited purpose of joining the first and second elastomeric seals together. A central portion of the coolant sealing segments can either comprise a hole to allow liquid to flow through the thickness of the plate, or alternatively, can comprise a solid portion that inhibits a flow of liquid through the thickness of the plate. The elastomeric element can be silicone rubber and the plate can be made of stainless steel. First and second graphite layers can be attached to the first and second surfaces of the plate.